New merocyanine dyestuffs

ABSTRACT

WHEREIN R is alkyl or aralkyl, X is oxygen or sulphur, m is 0 or 1, n is 0 or 1, p is 1 to 4 and D is the residue of a heterocyclic ring, electrophotographic material comprising said dyestuffs as sensitizers and a liquid sensitizer for electrophotographic material are disclosed.   New merocyanine dyestuffs of the formula

United States Patent 1 Brown et al.

[ 1 Sept. 18, 1973 I NEW MEROCYANINE DYESTUFFS [75] Inventors: David Sydney Brown; Geoffrey Ernest Ficken; Elizabeth Joan Treherne, all of Ilford, England [73] Assignee: Ilford Limited, Ilford, England [22] Filed: Oct. 22, 1971 [21] Appl. No.: 191,797

[ 30] Foreign Applic atlon Priority Data Oct. 27, 1970 Great Britain 51,031/70 [52] US. Cl 260/2948 D, 96/l.7, 260/240.4, 260/288 R, 260/306 R [SI] Int. Cl C09b 23/10 [58] Field of Search 260/306 R, 240.4, 260/294.8 D, 288 R 335,580 2/1959 Switzerland 260/306 Primary Examiner--John D. Randolph Attorney--E. F. Wenderoth et al.

[57] ABSTRACT New merocyanine dyestuffs of the formula wherein R is alkyl or aralkyl, X is oxygen or sulphur, m is 0 or I, n is 0 or l,p is l to 4 and D is the residue of a heterocyclic ring, electrophotographic material comprising said dyestuffs as sensitizers and a liquid sensitizer for electrophotographic material are disclosed.

2 Claims, No Drawings NEW MEROCYANINE DYESTUFFS This invention relates to novel merocyanine dyes, to their production and to their use for sensitising electrophotographic material.

According to the present invention there is provided a merocyanine dyestuff of the formula I wherein R is an alkyl or an aralkyl group, X is an oxygen or a sulphur atom, m is or I, n is 0 or l,p is 1 to 4 and D is the residue of a heterocyclic ring.

According to another feature of the present invention merocyanine dyestuffs of the above formula I are prepared by heating a merocyanine dyestuff of the formula II in which formulae R, X, m, n, p and D have the meanings assigned to them in formula I.

Merocyanine dyestuffs of the general formula I are of use as sensitizers for electrophotographic material. Electrophotographic material generally comprises a photoconductive layer coated on a support base which has been rendered at least partially electroconductive. Alternatively it comprises a photoconductive layer on an electroconductive layer which is in its turn coated on a support base. One of the most common photoconductive layers comprises zinc oxide particles in an insulating binder. Specially prepared zinc oxide which is photoconductive has to be employed and such zinc oxide is usually ultra-violet light sensitive, the sensitivity extending only a short distance into the visible light region of the spectrum. Colour electrophotographic material using zinc oxide photoconductive layers can be prepared and in this case the surface of the electrophotographic material usually comprises areas which have been selectively sensitized to the blue, green and red regions of the visible spectrum.

Therefore, according to another aspect of the present invention there is provided electrophotographic material which comprises a photoconductive layer which has been sensitized to a region or regions of the visible spectrum to which the photoconductive material is not in itself sensitive by the presence in the photoconductive layer of a merocyanine sensitising dye of the above general formula l.

The photoconductive layer is preferably photoconductive zinc oxide in a binder but it may be an organic photoconductor for example polyvinyl carbazole.

The electrophotographic material of the present invention may be prepared by coating a solution of one of the dyes of the above formula I directly on to the unsensitized photoconductive layer or particles of the photoconductive material, preferably zinc oxide, may have been sensitized by placing them in a solution of one of the above sensitizing dyes and drying and these sensitized particles may then be coated onto the electrophotographic material.

Preferably the electrophotographic material of the present invention is prepared by adding a solution of the dye to the coating mixture which comprises the photoconductive material, insulating binder, if present, and diluent liquid, before the coating mixture is coated onto the support base. When the photoconductive material is zinc oxide the solution of the dye may be added to the zinc oxide before it is mixed with an insulating binder, after it has been mixed with the binder but before dispersion, or it may be added to the coating mix ture containing the zinc oxide after dispersion.

Therefore according to another feature of the pres ent invention there is provided a liquid sensitizer for the sensitizing of electrophotogra-phic material which comprises an insulating liquid having suspended therein charged zinc oxide particles, said zinc oxide particles having been dyed with a merocyanine dyestuff of the above formula I.

Liquid sensitizers for the sensitizing of electrophotographic material are described in our co-pending Application No. 94,201, filed Dec. 1, 1970, now abandoned (corresponding to British Application No. 59 825/69).

A particular advantage of a class of merocyanines dyestuffs included within the above general formula I is that they are capable of sensitizing zinc oxide to the blue region of the spectrum.

Therefore, according to this aspect of the present invention there is provided electrophotographic material which comprises a zinc oxide photoconductive layer which has been sensitized to light of the blue region of the spectrum by the presence therein of a merocyanine dyestuff of the formula IV:-

where R, D, m, and .p have the meanings assigned to them in regard to Formula I.

The whole of the surface of the electrophotographic material may be sensitive to blue light by the presence therein of one of the dyes of the above Formula IV or selected regions only of the surface may be sensitive. In the latter case the surface of the photoconductive layer may comprise a mosaic of areas each of which has been selectively sensitized to one of the regions of the spectrum, blue, green and red.

The following Examples will serve to illustrate the invention. The temperatures are given therein in degrees centigrade.

EXAMPLE 1 l ',4-Dihydro-l '-methyl-4-pyridylidene )-2-( 3 sulphopropylthio)-2-thiazolin-4-one.

A mixture of 5-( l ,4'-dihydro-l '-methyl-4'- pyridylidene)-rhodanine (0.5 g) and l ,3 propanesultone 0.5 ml) was heated at 140 for 2 hours. The resulting product was cooled, ground with acetone, and the solid was filtered off, washed with acetone, dried and crystallised from water. The resulting dye had m.p. 307-309 (decomposition); the absorption maximum in methanol was 450 nm (log 6 4.67).

EXAMPLE 2 5-( 1 '-Ethyl- 1 ,4'-dihydro-4'-pyridylidene )-2-( 3 sulphopropylthio)-2-thiazolin-4-one.

The dye was prepared as in Example 1 from 5-(1'- ethyl-l ,4'-dihydro-4-pyridylidene)-rhodanine, and had m.p. 286 (decomp.) after crystallisation from water. The absorption maximum in methanol was 451 nm (log a 4.67).

EXAMPLE 3 5-( 3 -Ethyl-2 -benzothiazolinylidene )-ethylidene-2- (3 '-sulphopropylthio )-2-thiazolin-4-one.

The dye was prepared as in Example 1, heating 5-(3'- ethyl-2'-benzothiazolinylidene)-ethylidenerhodanine with 1,3-propanesultone for minutes. It was purified by washing with a little water, and had m.p. 259266; the asborption maxima in water were 5 39 nm (loge, 4.75) and 508 nm (log a, 4.66).

EXAMPLE 4 5-( 3 '-Ethyl-2 -benzoxazolidinylidene )-ethylidene-2- (3 '-sulphopropylthio )-2-thiazolin-4-one.

The dye was prepared and purified as in Example 3; it had m.p. 29l296, and the absorption maxima in water were 506 nm (log 6, 4.72) and 483 nm (log 6, 4.62).

EXAMPLE 5 EXAMPLE 6 5-(3'-Methyl-2'-thiazolidinylidene)-ethylidene-2-(3"- sulphopropylthio)-2-thiazolin-4-one.

The dye was prepared as in Example 5. The absorption maximum in water was 460 nm.

EXAMPLE 7 5-( 3 '-Methyl-2'-benzothiazolinylidene)-2-( 3 sulphopropylthio)-2-thiazolin-4-one.

The dye was prepared as in Example 5. The absorption maximum in water was 412 nm.

EXAMPLE 8 5-( l ,5 -Dimethyl-2-pyrrolidinylidene)-ethylidene-2- (3 '-sulphopropylthio )-2'-oxazolin-4-one.

A mixture of 5-( l ,5'dimethyl-2'-pyrrolidinylidene)- ethylidene-2-thio-2,4-oxazolidenedione 0.5 g) and 1,3-propanesultone (0.6 ml) was heated at 1 15 for 30 minutes. The cooled product was washed with several portions of cold ethyl acetate, to leave the dye as a sticky, hygroscopic solid. The absorption maximum in water was 418 nm.

EXAMPLE 9 5-( l ',4',4-Trimethyl-2'-pyrrolidinylidene)-ethylidene- 2-( 3 sulphopropylthio )-2-oxazolin-4-one.

The dye was prepared as in Example 8. The absorption maximum in water was 418 nm.

EXAMPLE 1O 5-( 1 '-Ethyl-3'-methylbenzimidazolinylidene )-2-(3"- sul-phopropylthio)-2-thiazolin-4-one.

A mixture of 1,3-propanesultone (0.24 g) and 5-( lethyl-3'-methylbenzimidazolinylidene )-rhodanine (0.30 g) was heated at for 2% hours. After cooling the product was triturated several times with dry ether and acetone to yield a hygroscopic dye; the absorption maximum in methanol was 387 nm (log e, 4.04).

EXAMPLE 1 1 5-( l ,2'-Dihydro-l -methyl-2-quinolylidene )-2-(3"- sulphopropylthio)-2-thiazolin-4-one.

The dye was prepared by heating 5-(l'-methyl-2'- quinolylidene)-rhodanine (0.82 g) with 1,3- propanesultone (1.1 g) at for 1% hours. The reaction product was purified, as described in Example 10, and the hygroscopic dye had an absorption maximum in methanol at 450 nm (log e, 4.10).

EXAMPLE l2 5-( 1 '-Ethyl-3'-methylbenzimidazolinylidene)-2-(4"- sulpho-butylthio)-2-thiazolin-4-one.

A mixture of 5-( 1 -ethyl-3 '-methylbenzimidazolinylidene)-rhodanine (0.20 g) and 1,4- butanesultone (0.36 g) were heated at 140 for 2 hours. After purification of the hygroscopic dye, as in Example 10, it had absorption maximum in methanol 390 nm (log 6, 4.10).

EXAMPLE 13' 5-( l '-Ethyll ,4-dihydro-4-pyridylidene )-2-(4 sulphobutylthio )-2-thiazolin-4-one.

The dye was prepared, as in Example 12, heating 5- l -ethyl'l ,4'-dihydro-4-pyridylidene)-rhodanine (0.5 g) with 1,4-butanesultone (1.80 g) for 4 hours. It was purified as in Example 10 and had m.p. 265; the absorption maximum in methanol was 453 nm (log 6, 4.65).

EXAMPLE 14 The following coating mixture was prepared:

Fotofax zinc oxide (ex Imperial Smelting Co.) 30 3 1387-09 resin (ex Cray Valley Products) 4.2 g Toluene 20 ml.

This coating mixture was ball-milled for five hours and then diluted with 15 ml toluene. 0.01 g of the dye of Example 2 was dissolved in 10 ml methanol and was added with stirring to the diluted coating mixture using a Silverson stirrer. When the dye had been thoroughly dispersed in the coating mixture, the coating mixture was coated on to an electroconductive paper base. A

similar photoconductive coating was prepared and coated on to an electroconductive paper base except that the above mentioned pyridylidene dye of Example 2 was not added. A wedge spectrogram of each material was then prepared. These spectrograms are shown in the accompanying figure. The unsensitised electrophotographic material is light-sensitive in the ultraviolet region of the spectrum but its sensitivity extends just into the blue region of the spectrum, the blue region commencing at 420 nm. On the other hand the bluesensitised material is also sensitive in the ultra-violet region of the spectrum but the sensitivity has in this case been extended to 470 nm. However the material has not been made sensitive to the green region of the spectrum, the green region commencing at 5 l0 nm.

EXAMPLE Further samples of electrophotographic material were prepared in a similar manner to those of Example 10 except that instead of the dye of Example 2 being used the dyes of the following Examples were used, Examples 3, 4 and 7 one dye to each sample of material.

A wedge spectrogram of each material was then prepared.

In the material which contained the dye of Example 3 the sensitivity had been extended to 610 nm with a maximum at 540 nm. The material had thus been sensitised to green light.

In the material which contained the dye of Example 4 the sensitivity had been extended to 550 nm with a maximum at 510 nm. The material had thus been sensitised so that its sensitivity extended part way into the green region of the spectrum.

In the material which contained the dye of Example 7 the sensitivity had been extended to 460 nm with a maximum at 425 nm. The material had thus been sensitised well into the blue region of the spectrum but had not been made sensitive to the green region of the spectrum.

We claim:

We claim: 1. A merocyanine dyestuff of the formula wherein R represents a methyl or ethyl group and p is 3 or 4. 

2. A merocyanine dyestuff according to claim 1 of the formula 